The traditional electrically operated lock, in particular a combination lock, commonly uses a lock clutch mechanism driven by a micromotor in order to save the space and reduce the energy consumption. One technical proposal is to adopt a spiral spring sleeved on a rotating shaft and a pin fixed on the rotating shaft, convert the rotary motion of the rotating shaft of the motor into the rectilinear motion between the spring and the pin, and then drive or pull the clutch mechanism or a latching mechanism of the lock to operate, and finally realize the control of the lock.
The U.S. Pat. No. 5,018,375 (Issue Date: Mar. 28, 1991) discloses a lockset having electric means for disabling and enabling the outer handle. The electric means is characterized in that: a transverse pin is arranged on a motor shaft; a spiral spring is sleeved on the shaft; one end of the spring is fixed on a clutch disc; the last two turns at the other end of the spring are tightly winded on the shaft; and the pin is just disposed between adjacent turns of the spring. When the motor shaft rotates, the pin is driven to move to the right of the spring along a spiral of the spring; the function of the spring on the pin in the process is a nut; and the clutch disc is pulled by the spring for engagement. When the motor shaft rotates counterclockwise, the pin is driven to move to the left of the spring along the spiral of the spring and the clutch disc can be driven for disengagement.
The Chinese patent No. ZL01243139 (Issue Date: May 15, 2002) discloses a sliding plate push-and-pull displacement electric mechanism for a lock, which is characterized in that: a slider capable of performing axial movement and a spring capable of driving the slider to move are sleeved on a rotating shaft; both ends of the spring are extended into an axial groove of the slider along the radial direction; a cotter pin is fixed in the middle part of the rotating shaft; and both ends of the cotter pin are extended along the radial direction and can be screwed into two adjacent turns of the spring, so that the spring is driven to rotate clockwise and counterclockwise along the cotter pin and move back and forth on the shaft.
As the same with numerous technical proposals of combination locks, the motor adopted by the above technical proposal is a common DC micromotor. Due to the parameter decentrality during the motor manufacturing and the voltage variation of supplying cells, the rotating speed error of the motor may be large, and the travel of the pin on the rotating shaft is difficult to control even by adopting a reducing gear train and controlling the conduction time. Therefore, in most cases, the pin moves to the end part (the final turn) of the spring and may perform circulating rotation at the position as no spiral is provided for the pin to move along.
When the pin performs relative motion along the spiral of the spring, the spring is compressed due to the pressure of the pin and large friction is generated, and finally a force which drives the spring to rotate along with the shaft is generated due to the friction. Particularly, in the case of abnormal unlocking or locking, for example, a lock handle is pulled at the moment or the lock handle is pulled first and then an unlocking command is input when the motion of the clutch mechanism is not in place, common manual operation errors like this will result in the clamping of the slider driven by the spring and then possible complete compression of the spring. Herein, the friction force is maximized and the extrusion of adjacent turns of the spring is generated, thus not only the spring tends to rotate along the shaft but also the pin cannot enter into a spiral track of the spring when the motor is started counterclockwise, consequently unlocking or locking failures are produced. Moreover, after the pin is disposed at a limiting position of one end, the next motion is the reversing rotation of the pin. As no buffer mechanism is arranged, the spring will jitter or bounce due to the impact of the pin on the spring when the motor is started counterclockwise, thus the failure that the pin cannot smoothly enter into the spiral track of the spring after the rotating shaft changes the rotation direction may be caused, consequently the clutch mechanism for the lock fails.